Calendar Mechanism For Displaying The Date And The Day Of The Week In One Timepiece

ABSTRACT

A calendar mechanism for displaying the date and the day of the week in a timepiece, including a date indicator in the form of an internally toothed crown, means for driving said date indicator including a first drive wheel having an external toothing so as to be able to be driven about an axis of rotation by a wheel set secured to an hour wheel of the timepiece and said toothing including a prominent tooth, longer than the others, which abuts against a tooth of the inner toothing of the date indicator to move it forward one day in a time interval located around a determined time of the day, said mechanism also including a day of the week indicator, means for driving said day of the week indicator to move it forward one day during said time interval and means for positioning said indicators.

The present invention concerns a calendar mechanism for displaying thedate and the day of the week in a timepiece, including a date indicatorin the form of an internally toothed crown, means for driving saidindicator including a first drive wheel having an external toothing soas to be able to be driven about a rotational axis by a wheel setsecured to an hour wheel of the timepiece and said toothing including aprominent tooth, longer than the others, which abuts against a tooth ofthe inner toothing of the date indicator to make it move forward one dayin a time interval at around a determined time of the day, thismechanism also including a day of the week indicator, means for drivingsaid day of the week indicator to make it move forward one day duringsaid time interval and means for positioning said indicators.

A mechanism of this type, similar to that which forms part of certainwatch movements that are already manufactured and marketed by theApplicant is shown in an exploded perspective view in FIG. 1, as well asother elements of the movement which are directly related to thismechanism.

Among these elements there is an hour wheel 2 mounted at the centre ofthe movement and making one revolution in 12 hours, the pipe 4 of whichis for carrying an hour hand that is not shown.

A pipe 6 of a minute wheel, itself surrounding an axis 8 of a secondwheel, can rotate inside this pipe 4, said pipe 6 and said axis 8 beingprovided for respectively carrying a minute hand and a second hand whichare also not shown.

On pipe 4 of hour wheel 2 and in contact with said wheel there is fixeda pinion 10 with six teeth 12, which meshes with a drive wheel 16. Inorder to make one revolution in 24 hours, this drive wheel, which pivotsabout a fixed arbour 14 of the movement and which includes twelve teeth18, is solely responsible for driving both a day of the week disc 20secured to a day star-wheel 22 and a date crown 24, in a manner thatwill be explained hereinafter.

Among the elements of the movement directly related to the datemechanism there is also a plate 26 that is partially shown, whichincludes an upper edge 28 that acts as a support for a dial 30 providedwith an aperture 32. This plate 26 which allows dial 30 to be axiallypositioned, is also used for positioning it angularly by means that arenot shown, such that its aperture 32 is located at 3 o'clock to allowthe user of the watch containing the movement to read the day of theweek and the date of the day correctly through the aperture.

Moreover, plate 26 also acts as a support for date crown 24, which issurrounded and held in place radially by edge 28 of the plate.

As the drawing shows, the day disc 20 which carries abbreviations of theseven days of the week twice in the same language and the day star-wheel22 which consequently includes fourteen teeth 34, are mounted so as tobe able to pivot about pipe 4 of hour wheel 2 and held in place axiallyby a key 36, the assembly of disc 20 and star-wheel 22 being able to beachieved for example by riveting or laser welding.

As regards date crown 24, which can be obtained by cutting and folding asheet metal or a thin metal strip, it has a stair shaped profile andincludes three concentric annular parts 38, 40 and 42, whose leveldecreases from the outside inwards.

The first annular part 38, whose contour corresponds to that of thecrown, carries numbers from 1 to 31 regularly distributed over itssurface. The second part 40, which receives day disc 20, has a slightlylarger diameter than that of the disc so as not to disturb its rotationand the difference in level between this second part and the first issuch that the day of the week and the date appear substantially in thesame plane and close to each other in aperture 32 of dial 30. Third part42 has an inner toothing which includes 31 radial teeth of isoscelesshape 44 which correspond to the 31 days of the longest months.

The calendar mechanism of the movement of FIG. 1 also includes a holdingplate 46 inserted between day disc 20 and third part 42 of date crown24, which is fixed by means of screws 48 to a fixed part of themovement. This plate 46 has three functions. The first and secondconsist in holding drive wheel 16 and date crown 24 axially withoutdisturbing their mobility. The third function is to act asjumper-springs for date crown 24 and for day star-wheel 20. In order todo this, plate 46 is cut and bent so as to form a first elastic tongue50, which extends below the plane of the main part of the plate andwhich ends in a V-shaped end, pointed towards the exterior of themovement to be engaged between teeth 44 of date crown 24 and a secondelastic tongue 52 extending above the plane of said plate 46 and whichalso ends in an end part that is V-shaped, but pointed towards theinside of the movement to be engaged between teeth 34 of day star-wheel22, which are both radial and isosceles shaped.

In order to describe drive wheel 16 and the operation of the calendarmechanism of FIG. 1 in detail, reference will also be made to FIG. 2,which shows wheel 16 in perspective again but on a larger scale.

This wheel 16 includes a hub 54 via which it is mounted on arbour 14 andwhich is connected by a spoke-shaped connecting element 56 to a crown 58which carries the aforementioned teeth 18.

Among these teeth 18 there is a prominent tooth 18′ which extendsradially beyond the others so as to be the only one able to be engagedbetween teeth 44 of date crown 24 while being able to be engaged likethe others between teeth 12 of pinion 10. For a reason that will beunderstood hereinafter, this tooth 18′ has a flank called the “frontflank” 60 of the same inclination as the flanks of the other teeth, i.e.substantially radial, and a “back flank” 62 which, at the end of thetooth intended to be engaged between teeth 44 of crown 58 has an obliqueface 64 of smaller inclination to form an acute angle with front flank60.

This having been said, wheel 16 also includes an elastic arm 66 more orless shaped in the arc of a circle, integral with the other elements ofwheel 16, attached to hub 54 and extending inside toothed crown 58. Thisarm has, at its free end, a first tongue of substantially rectangularshape and bent at 90° towards the front of the movement so as to form adrive finger 68 able to be engaged between teeth 34 of day star-wheel22. Moreover, arm 66 and the orientation of drive finger 68 with respectto the flanks of teeth 34 are provided such that the arm is onlydeformed significantly when it is forced to move away from hub 54 ofwheel 16 and very slightly in the opposite direction.

Finally, wheel 16 also includes a second tongue 70 of substantiallyrectangular shape, made in one piece with elastic arm 66, located in theplane of the wheel, at a certain distance from the end of the arm andextending in the direction of crown 58. The usefulness and advantage ofthis second tongue which is not involved in the operation of thecalendar mechanism of FIGS. 1 and 2, will be specified hereinafter.

The calendar mechanism of FIGS. 1 and 2 is of the dragging type, i.e.the movement of the date forward one unit and passage from one day ofthe week to the next occur over a period of approximately four hoursaround midnight.

While the movement is operating normally, outside this time period, itsmotor, whether it is of the purely mechanical or electromechanical type,drives pinion 10 in the clockwise direction and calendar drive wheel 16in the anti-clockwise direction indicated by arrow F1 in the drawing.During this time period, wheel 16 does neither mesh with date crown 24nor with day star-wheel 22 whose positions are determined and maintainedby jumper-springs 50 and 52 such that the indications of the date andday of the week appear properly framed in the aperture of dial 30 andwithout any shocks that the movement undergoes being able to alter saidindications.

For a reason that will be explained hereinafter, drive wheel 16 isdesigned such that there is a certain phase shift, for example ofapproximately half an hour, between the start of driving day disc 20 andthat of date crown 24 or conversely. Hereinafter, it will be assumedthat we are in the first of these situations to describe the operationof the calendar mechanism of FIGS. 1 and 2 and a variant thereof that isalso known and that of the mechanism according to the invention.

In these circumstances, when drive finger 68 comes into contact with theback flank of a tooth 34 of day star-wheel 22, the finger starts toexert a torque on said tooth 34, which is opposed by the action ofjumper-spring 52. Gradually as drive wheel 16 rotates in the directionof arrow F1, elastic arm 66 becomes taut moving away from hub 54 andfinger 68 slides along the flank of tooth 34 with which it is in contactand rotates star-wheel 22 and day disc 20 in the direction of arrow F2.At the same time, the end of jumper-spring 52 comes out of the hollowbetween two teeth of star-wheel 22 in which it was located, while thetorque exerted by finger 68 on tooth 34 increases.

Approximately half an hour after the star-wheel and the day disc startto be driven, front flank 60 of tooth 18′ of wheel 16 comes into contactwith the back flank of a tooth 44 of date crown 24 and then starts toslide over this back flank and to rotate the date crown in the directionof arrow F3, i.e. in the same direction as drive wheel 16 and in theopposite direction to that in which day disc 20 is rotating. During thistime, the end of jumper-spring 50 starts to come out of the hollowbetween two teeth 18 of the date crown in which it was located, saidspring starts to tighten and the torque exerted by tooth 18′ on tooth 44with which it is in contact starts to increase.

During the period that follows, which is the longest of the timeinterval necessary to change the day and the date, wheel 16simultaneously drives day star-wheel 22 and date crown 24 supplying ahigher torque than that of the sum of the resistant torques exerted byjumper-springs 50 and 52 respectively on tooth 34 of day star-wheel 22and that 44 of date crown 24 with which tooth 18′ and tooth 34 of daystar-wheel 22, these torques continuing to increase until the end ofjumper-spring 52 reaches the tip of tooth 34 of day star-wheel 22.

In a very short instant, spring 52 is let down when its tip descendsinto the hollow of day star-wheel 22 following that between the teeth ofwhich it was previously located, in the direction of arrow F2. At thesame moment, drive finger 68 of arm 16 is ejected from the toothing ofday star-wheel 22 while it was exerting a maximum torque on the latterand the day of the week indicated by disc 20 finishes passing to thenext day.

A little later, the same process occurs for jumper-spring 50, the hollowbetween teeth 44 of date crown 24 between which its end was located andlong tooth 18′ of drive wheel 16, which means that the date indicationmoves forward one unit.

Thus, owing to the phase shift between driving the day disc and that ofthe date crown, the total torque provided by the drive wheel 16 neverreaches the sum of the maximum torques exerted by said wheel on the daystar-wheel and the date crown, which prevents the movement drive motorlocking or at lest the disc and/or the crown moving backwards.

When an alteration of the date indication in particular during passagefrom a month of thirty days or less in the case of February to the nextmonth, or an alteration both of the date and the day of the weekindication, for example when the battery is changed in the case of anelectromechanical movement or an extended lack of winding in the case ofa mechanical watch, this or these changes can occur manually and quicklyby means of a control stem and a correction mechanism that are not shownin the drawing. In the case of movements marketed by the Applicant, asin many others, the control stem is a stem which can be placed in threeaxial positions, a neutral or winding pushed-in position, a first pulledout position in which the date display can be altered by rotating thestem in one direction and the day of the week display by rotating thestem in the other direction and a second pulled out position reservedfor setting the time of the hands of the watch.

When the date is set outside the time interval when neither the day discnor the date crown are being driven by wheel 16, this does not cause anyproblems. However, very often, setting the day and more frequentlysetting the date occurs around midnight, i.e. during this interval.

When an alteration of the date occurs in these circumstances, the datecorrection mechanism non shown acts on teeth 44 of date crown 24 so asto rotate the latter in the direction of arrow F3, against jumper-spring50 and each time that the front flank of a tooth 44 comes into contactwith the oblique face 64 of the back flank of tooth 18′ of drive wheel16, this front flank of a tooth 44 slides over this oblique face oftooth 18′ without substantially altering the angular position of tooth18′, owing to the natural elasticity drive wheel 16 which is then veryslightly deformed and against the resistant torque then exerted on saidwheel 16 by pinion 10, which rotates in the opposite direction at a muchlower speed, which can even be considered to be zero.

In the case where, more rarely, the position of the day disc also has tobe altered during the time interval in question, the correctionmechanism drives day star-wheel 22 in the direction of arrow F2 makingthe end of jumper-spring 52 jump from a hollow between two teeth 34 tothe next one. When a front flank of a tooth of day star-wheel 22 comesinto contact with drive finger 68, it forces elastic arm 66 to curvevery slightly in the direction of hub 54 of wheel 16 to return then toits initial position after finger 68 has passed to the tip of tooth 22.

Moreover, if the time is altered forwards, everything occurs in the sameway as when the mechanism is operating normally, except that if thisalteration occurs while the day and date change process is in progress,this process is accelerated during the period in which the time is beingaltered. However, if the time change occurs backwards, wheel 16 rotatesin the opposite direction to that of arrow F1. In this case, whenoblique face 64 is or comes into contact with a tooth 44 of the datecrown, this tooth slides or continues to slide over this face, whichcauses or maintains a slight deformation of the crown of wheel 16 whichmeans that the position of the wheel remains unchanged. When, during thesame period, the back face of tooth 68 comes into contact with a tooth34 of day star-wheel 22, this tooth slides over the back face which onlycauses a very slight deformation of arm 66 in the direction bringing itback to hub 54 of the wheel until tooth 68 reaches the tip of tooth 34.At that moment, the arm returns to its initial position without theposition of star-wheel 22 and day disc 20 having been altered.

FIGS. 3 and 4 illustrate a variant of the calendar mechanism shown inFIGS. 1 and 2, which corresponds to a mechanism used in other movements,also manufactured and marketed by the Applicant.

As shown in FIG. 3, which is a top view of the day of the week disc andthe day star-wheel, this star-wheel still being designated by thereference numeral 22 remains unchanged and still includes fourteen teeth34.

However, day disc 20′ no longer carries abbreviations of the successivedays of the week twice in the same language, like disc 20 of FIG. 1, butalternatively, the abbreviations of the days in two languages, in thisparticular case, in English and French.

Consequently, in order always to have the day displayed in the samelanguage, the day star-wheel and disc must no longer rotate normally byone fourteenth of a revolution per day, but by a seventh. In order to dothis, the second tongue 70 of drive wheel 16 shown in FIGS. 1 and 2simply has to be bent to make a second drive finger 70′, as shown inFIG. 4. Thus, after first finger 68 has acted on a tooth 34 of daystar-wheel 22 to rotate day disc 20′ by a fourteenth of a revolution,second drive finger 70′ acts in the same way on the following tooth 34to rotate the disc again by a fourteenth of a revolution in the samedirection.

As for first finger 68 and for the same reason, the action of secondfinger 70′ is synchronised with that of tooth 18′ so that the totaltorque that drive wheel 16 has to exert at the same time on daystar-wheel 22 and date crown 24 never reaches the sum of the maximumtorques necessary to rotate the star-wheel and the crown.

Moreover, when the day of the week is changed manually, second finger70′ acts like first finger 68, i.e. it forces elastic arm 66 to curve toallow star-wheel 22 and day disc 20′ to pass to the display of a sameday in one language to another, or from one day to the next in the samelanguage.

Naturally, everything that has previously been said with respect tofirst drive finger 68 and arm 66 is also valid for second drive finger70′.

Furthermore, this variant of FIGS. 3 and 4 justifies the presence oftongue 70 in the embodiment of FIGS. 1 and 2. In fact, in order to makedrive wheels 16 that can be used in both cases, one need only cut flatparts having the two tongues for forming the two drive fingers 68 and70′ from a metal strip or plate, and bend only one of the tongues orboth to obtain wheels which can be used either in the embodiment ofFIGS. 1 and 2, or in its variant, which evidently constitutes a saving.

Despite this, this embodiment of FIGS. 1 and 2 and its variant havecertain drawbacks.

First, wheel 16 made in a single piece of the same material does notallow optimum driving of both the day star-wheel and the date crown tobe obtained as a function of the materials of which they may be formed,for example when the date crown is made of a copper and beryllium alloywhereas the day star-wheel is made of steel to allow a day disc to belaser welded onto said star-wheel.

Secondly, for a given movement, the phase shift sign and value betweenthe driving of the day disc and that of the date crown are determinedwhen drive wheel 16 is designed and manufactured. For various reasons,it may be preferable to start by driving the date crown rather than thestar-wheel and the day disc and not necessarily with the same forwardmovement. In the case of the known mechanisms of FIGS. 1 to 4, this canonly be achieved by replacing wheel 16 with another wheel.

Finally, thirdly, in these known mechanisms of FIGS. 1 to 4, drive wheel16, which is actually very thin, has to drive both the date crown andthe day star-wheel for a long time in opposite directions, which meansthat it is then subjected to quite significant stress which can greatlylimit is life time and the proper operation or even just the operationof the calendar mechanism of which it forms a part.

It is an object of the invention to provide a calendar mechanism capableof indicating both the date and the day of the week, which does not havethese drawbacks.

This object is attained owing to the fact that the mechanism accordingto the invention, which answers the definition given in the firstparagraph hereinbefore, is characterised in that the day of the weekindicator drive means include a second drive wheel provided with anexternal toothing, superposed with and coaxial to the first drive wheeland in that said first and second drive wheels have the same diameterand the same even number of teeth and are driven by the same wheel setsecured to the hour wheel.

Preferably, said drive wheel is formed by a pinion fixed onto a pipe ofsaid hour wheel and including a number of teeth equal to half that ofsaid first and second drive wheels.

Other features and advantages of this mechanism will appear upon readingthe following description of two possible embodiments, a descriptionthat refers to the annexed drawings, among which:

FIGS. 1 to 4, already defined hereinbefore, illustrate the state of theart, which, to the Applicant's knowledge, is the closest to theinvention;

FIG. 5 is an exploded perspective view of a first possible embodiment ofa mechanism according to the invention;

FIG. 6 is also an exploded perspective view of a second possibleembodiment of the mechanism according to the invention; and

FIGS. 7 and 8 are plan and top views of two drive wheels of themechanism of FIG. 6.

By comparing FIGS. 5 and 6 to the known variant illustrated by FIGS. 3and 4 of the calendar mechanism that is also known, shown in FIG. 1, itwill be observed that apart from drive wheel 16, FIGS. 5 and 6 show notonly all of the parts of the mechanism according to this variant, butalso partially show those watch movement elements that are related tosaid mechanism

It is thus unnecessary to describe again all of the common parts whichare designated in FIGS. 5 and 6 by the same references as in thepreceding Figures.

This having been said, the embodiment of the mechanism according to theinvention shown in FIG. 5 differs from the variant in question in thatthe single drive wheel 16 of that variant is replaced by two superposedcoaxial wheels 76 and 76′, having the same diameter and the same numberof teeth, respectively 78 and 78′, in this particular case twelve teeth,which are both mounted on the same arbour 14 secured to the frame of themovement and driven by the same pinion 10 with six teeth secured to pipe4 of hour wheel 2 of this movement.

Naturally, although they are designated by the same reference numeralsand that there is no longer only one calendar drive wheel but twosuperposed wheels, the height of arbour 24 and the thickness of pinion10 can be greater than that which they had in the known embodiment andvariant previously described. For the same reason, the exact shape ofplate 46, which allows these two wheels to be held in place, could beslightly altered, at least locally.

Moreover, as it is shown in FIG. 5, wheel 76 which is responsible fordriving date crown 24 includes, like wheel 16 of FIGS. 1 to 4, a hub, aspoke and a tooth crown that are unreferenced. However, it no longerincludes an elastic arm nor fingers for driving star-wheel 22 and daydisc 20, which means that it could be made in another form provided thatit continues to have, on the one hand, a longer tooth 78′ than theothers and of the same shape as previously so as to be able to drive thedate crown and, on the other hand, sufficient natural elasticity toallow manual alteration of the date display in the same way as with thesingle drive wheel 16.

As regards wheel 76′, which is located above the date drive wheel andwhose role is to drive star-wheel 22 and day of the week disc 20, it isidentical to wheel 16 of FIG. 2, except that it does not include anyparticular teeth and its twelve teeth 78′ are identical.

It is thus unnecessary to describe the operation of the calendarmechanism according to the invention shown in FIG. 5. However, it isuseful to show that this mechanism or a similar mechanism enable theaforementioned desired objects of the invention to be attained.

In fact, in such a mechanism, parameters for each of wheels 76 and 76′,like the material of which they are formed, the shape of their teeth ortheir resistance to wear, can be determined separately as a function ofthe structural features and manufacturing methods of the wheel setswhich they drive in order to optimise the operation of the calendarmechanism of which they form part.

Moreover, the mechanical stress experienced by wheels 76 and 76′ whichare also very thin and fragile but which only drive one wheel set eachand in a single direction is much less than that experienced by a singlewheel which drives two wheel sets rotating in opposite directions.

Furthermore and unlike the known mechanisms of FIGS. 1 to 4, the drivingof the star-wheel and day disc can no longer have any negative influenceon the elastic behaviour of the toothed drive crown of date crown 24 andvice versa.

Finally, in the case of the embodiment of the mechanism according to theinvention of FIG. 5, it is easy to mount wheels 76 and 76′ on arbour 14such that star-wheel 22 and day disc 20 start to be driven before datecrown 24 or vice versa. However, given that pinion 10 secured to hourwheel 2 only includes six teeth and drive wheels 76 and 76′ twelveteeth, it is not possible to increase or decrease the time intervalbetween the instants when said star-wheel and said day disc, on the onehand, and said date crown on the other hand, start to be driven, thisinterval necessarily remaining the same as for the known mechanism ofFIGS. 1 to 4. However, in the case of the mechanism according to theinvention, there exists a simple solution for solving this problem. Thissolution consists in multiplying to a certain extent the number of teethof pinion 10 and wheels 76 and 76′, while keeping a ratio of 2:1 betweensaid wheels and said pinion. As regards the known mechanisms of FIGS. 1to 4, it would also be possible to increase the number of teeth ofpinion 10 and wheel 16, which is actually the case in the real movementsalready manufactured and marketed by the Applicant, but with a singledrive wheel for the calendar mechanism this would not solve the problem.

As in the embodiment of FIG. 5, in the embodiment shown in FIG. 6, themechanism according to the invention includes two superposed coaxialwheels 80, 80′ having the same diameter and the same number of teeth,respectively 82 and 82′, also twelve in number, mounted on the samearbour 14 secured to the movement frame and driven by the same pinion 10with six teeth, secured to hour wheel 2 of the movement.

As FIG. 7 shows more clearly, wheel 80, provided for driving date crown24, includes a hub 84 from which there extends a substantially radialwide arm 86. From the end of this radial arm 86 there extends anelastically deformable arm 88 substantially in the shape of an arc of acircle, which extends in the normal rotational direction of wheel 80,indicated by arrow F1, and which surrounds most of hub 84 to be attachedvia the inside and via a substantially radial and rigid connecting part90 to a crown 92, which carries the teeth 82 of the wheel.

Like the toothed crown of drive wheel 76 of the embodiment of FIG. 5,crown 92 has a particular prominent tooth 82″ that is longer than theothers so as to be able to be engaged between teeth 44 of date crown 24(see FIG. 6) and which has the same orientation and the same shape asthe prominent teeth of the drive wheels and date crowns discussedhereinbefore.

However, in the embodiment of FIG. 6, this tooth 82″ is no longerattached to normal tooth 82 which precedes it when wheel 80 is rotatingin the direction of arrow F1, but is separated from the latter by a cut94.

Thus, when the calendar mechanism is operating normally, and when frontflank 96 of tooth 82″ comes into contact with the back flank of a tooth44 of date crown 24, said crown does not immediately start to be drivenby tooth 82″. Despite the motor torque exerted by pinion 10 on drivewheel 80 to rotate it in the direction of arrow F1 and because of aresistant inertial and friction torque exerted on the wheel in theopposite direction, tooth 82″ starts by remaining still, which meansthat the spring formed by elastic arm 88 is wound until a substantiallyradial front flank 102 of connecting part 90 comes into contact with acorresponding back flank 104 of radial arm 86 joining hub 84 to elasticarm 88. During this time, the width of cut 94 of the wheel increases.

From the moment when the contact is established between front flank 102of connecting part 90 and back flank 104 of arm 86, particular tooth 82″starts to drive date crown 24 in the same manner as tooth 78″ of wheel76 in the embodiment of FIG. 5, until said tooth 82″ crosses tooth 44 ofthe date crown with which it was in contact and falls down into the nexthollow of the date crown toothing, which enables elastic arm 88 to belet down.

Thus, in the case of the embodiment of FIG. 6 and as regards the drivingof the date crown, the mechanism according to the invention is no longerof the dragging type, but is semi-dragging or, which amounts to the samething, semi-instantaneous, which means that the change of dateindication is quicker than in the embodiment of FIG. 5, the time of thischange being able to be reduced roughly by half.

This having been said, when a quick alteration occurs to the dateindication in response to a manipulation of a control stem and when atooth 44 of date crown 24 comes into contact with the oblique face 100of tooth 82″, said date crown tooth 44 exerts a torque on tooth 82″which tends to rotate first drive wheel 80 in the direction of arrow F1.However, since pinion 10, which can then be considered immobile, opposessuch a rotation, date crown tooth 44 slides over the oblique face 100,which only causes a slight tension in elastic arm 88 and a slightdecrease in the width of cut 94 of crown 92 and as soon as tooth 44passes the tip of tooth 82″, drive wheel 80 returns to its originalform.

Likewise, when pinion 10 rotates in the opposite direction to that ofarrows F1 and F3 to enable a backward adjustment to the time setting ofthe timepiece, and when oblique face 100 of tooth 82″ of wheel 86, whichis then rotating in the opposite direction to that of the pinion, comesinto contact with a date crown tooth 44, the torque exerted by tooth 82″on this tooth 44 is not enough to alter the position of the date crownand elastic arm 88 and cut 94 of crown 92 behave in the same way aspreviously.

As FIG. 8 shows, wheel 80′ for driving star-wheel 22 and day of the weekdisc 20 includes a hub 106, a crown 108 carrying teeth 82′ and connectedto hub 106 by a spoke 110, an elastic arm 112, substantially in theshape of an arc of a circle, which surrounds a part of hub 106 and whichcarries two drive fingers 112 and 114 formed and arranged in the sameway as drive fingers 68 and 70′ of drive wheel 16 shown in FIG. 4 andwhich forms part of the known calendar mechanism variant of FIG. 1.

Finally, elastic arm 112 of drive wheel 80′ shown in FIG. 8 also carriesa substantially radial support finger 118 located in the plane of saidwheel which extends towards crown 108 and which ends in a rounded endpart 120.

When wheel 80′ is being driven normally in the direction of arrow F1 andwhen drive finger 114 comes into contact with the back flank of a tooth34 of day star wheel 22 and starts to exert a torque on the tooth,elastic arm 112 tightens and moves away from hub 106 until end 120 offinger 118 abuts against the inner edge 122 of crown 108. During thistime, first drive finger 114 pushes on the day star-wheel tooth slidingover the front flank of said tooth to its tip and from the moment whenfinger 118 comes into contact with inner edge 122 of the crown, thetorque exerted by finger 114 on tooth 34 is practically at a maximum.Next, when finger 114 has passes the tip of tooth 34 of day star-wheel22, it falls back into the hollow of star-wheel 22 following thatbetween the teeth of which it was previously located and after the daystar-wheel has rotated one fourteenth of a revolution, elastic arm 112is let down.

The same thing occurs when second drive finger 116 rotates the daystar-wheel again by one fourteenth of a revolution in the same directionand when wheel 80′ is quickly driven again in the same direction toalter the indication of the day of the week by a manual command.

Moreover, it goes without saying that everything that was previouslyexplained in relation to the direct alteration, or alteration via a timesetting stem, remains valid with certain obvious adaptations, for theembodiment of FIGS. 6 to 8.

Finally, to conclude with the embodiment of FIGS. 6 to 8, it should bespecified that finger 118 also acts as a limit stop for crown 92 ofdrive wheel 80 of date crown 24 arranged below drive wheel 80′ ofstar-wheel 22, in order to prevent any possible blocking between thesetwo wheels which are very thin and which can be deformed while theyrotate.

This having been said, it is evident that the invention is not limitedto the two embodiments that have just been described.

For example, the day disc in two languages could be replaced by a discin a single language like that of FIG. 1. In such case, the drive wheelfor the disc would only have a single drive tooth.

Moreover, the day disc could carry the days of the week only once andthe day star-wheel could include only seven teeth.

On the other hand, the same disc and star-wheel could display the daysin three languages.

As regards the drive pinion secured to the pipe of the hour wheel andthe drive wheels of the date crown and the day disc, the number of theirteeth could be less than or more than respectively six and twelve, theessential point being that the ratio of 2:1 is maintained between thesenumbers.

Of course, these are only examples since many other embodiments orvariants can be imagined without departing from the scope of theinvention.

1-12. (canceled)
 13. A calendar mechanism for displaying the date andthe day of the week in a timepiece, including a date indicator in theform of an internally toothed crown, means for driving said dateindicator including a first drive wheel having an external toothing soas to be able to be driven about an axis of rotation by a wheel setsecured to an hour wheel of said timepiece and said toothing including aprominent tooth, longer than the others, which abuts against a tooth ofthe inner toothing of the date indicator to move it forward one day in atime interval located around a determined time of the day, saidmechanism also including a day of the week indicator, means for drivingsaid day of the week indicator to move it forward one day during saidtime interval and means for positioning said indicators and saidmechanism being wherein said means for driving the day of the weekindicator include a second drive wheel fitted with an external toothing,superposed and coaxial to the first drive wheel and wherein said firstand second drive wheels have the same diameter and the same even numberof teeth and are driven by the same wheel set secured to said hourwheel.
 14. The calendar mechanism according to claim 13, wherein saiddrive wheel is formed by a pinion secured to a pipe of said hour wheeland including a number of teeth equal to half of that of said first andsecond drive wheels.
 15. The calendar mechanism according to claim 14,wherein said day of the week indicator is a disc coaxial to said dateindicator and wherein said means for driving said disc include a daystar-wheel secured to said disc and driven by said second drive wheel.16. The calendar mechanism according to claim 15, wherein said seconddrive wheel pivots on a fixed arbour and includes a hub via which it ismounted on said arbour and which is connected to a crown carrying saidteeth and an elastic arm substantially in the shape of an arc of acircle, attached at least indirectly to said hub and partiallysurrounding the latter, and wherein said elastic arm has at its free enda first drive finger substantially perpendicular to the plane of saidsecond wheel which is engaged between the teeth of said day star-wheelto move said day of the week indicator disc forward one day of the weekwhen said calendar mechanism is operating normally.
 17. The calendarmechanism according to claim 15, wherein the day of the week indicatordisc carries alternately abbreviations of the names of the days of theweek in two different languages, wherein said day star-wheel includesfourteen teeth, wherein said elastic arm has a second drive finger alsosubstantially perpendicular to the plane of said second drive wheel andwherein said second drive finger is located in relation to the firstfinger such that said drive fingers act one after the other on twosuccessive teeth of said day star-wheel in order to rotate said day ofthe week disc twice by a fourteenth of a revolution in the samedirection during said time interval located around a determined time ofthe day.
 18. The calendar mechanism according to claim 16, wherein saidelastic arm also carries a substantially radial support finger locatedin the plane of said second drive wheel and having one end which abutsagainst said crown of said second drive wheel when said elastic arm isdeformed in the direction of said crown practically at the moment whensaid deformation is sufficient to allow said first drive finger to movesaid day of the week indicator disc forward one day, against saidpositioning means.
 19. The calendar mechanism according to claim 16,wherein said elastic arm, said first drive finger, said teeth of the dayof the week star-wheel and said means for positioning said star-wheelare designed such that said first drive finger slides over one of saidteeth without any significant deformation of said elastic arm, in thedirection of said hub and owing to a natural elastic deformation of saidcrown so that said day of the week indication is not altered when saidpinion rotates in an opposite direction to that which allows it to drivesaid second drive wheel and said day star-wheel in their normalrotational directions.
 20. The calendar mechanism according to claim 14,wherein said first drive wheel pivots on a fixed arbour and includes ahub via which it is mounted on said arbour and which is connected to acrown carrying said teeth by a radial arm.
 21. The calendar mechanismaccording to claim 20, wherein said prominent tooth of the first drivewheel has a substantially radial front flank like the other teeth ofsaid wheel which acts each time on a tooth of said date crown to moveforward the date indication one day when the mechanism is operatingnormally and a back flank which, at the end of said prominent toothprovided for engaging between the teeth of said date crown, has anoblique face of smaller inclination to form an acute angle with saidfront flank and to allow said first drive wheel, which is thenelastically deformed, to rotate in the opposite direction to its normalrotational direction without altering the date indication, when it isdriven in the opposite direction by said pinion.
 22. The calendarmechanism according to claim 14, wherein said first drive wheel pivotson a fixed arbour and includes a hub from which extend a wide radialarm, an elastically deformable arm substantially in the shape of an arcof a circle, starting from a free end of said arm and extending in thenormal rotational direction of said first drive wheel, said elasticallydeformable arm surrounding most of said hub to be attached via theinterior and a substantially radial and rigid connecting part to a crownwhich carries said teeth; wherein said prominent tooth of the firstdrive wheel is separated from the tooth that precedes it when said wheelrotates in its normal rotational direction by a cut of said crown; andwherein, when said wheel rotates in the normal direction and when saidprominent tooth comes into contact with a tooth of said date crown todrive the latter, said prominent tooth starts by remaining still whilesaid elastically deformable arm tightens in the direction which bringsit closer to said hub and that the width of said cut increases, until afront flank of said connecting part comes into contact with a back flankof said radial arm and said prominent tooth comes into contact with thetooth which precedes it, after which said prominent tooth drives saiddate crown to move it forward one day and then allow said drive wheel toreturn to its original form.
 23. The calendar mechanism according toclaim 22, wherein said prominent tooth of the first drive wheel has asubstantially radial front flank like the other teeth to move the dateindication forward one day when the mechanism is operating normally anda back flank which, at the end of said prominent tooth provided forengaging between the teeth of said date crown, has an oblique face ofsmaller inclination to form an acute angle with said front flank andwherein when said first drive wheel is driven in the opposite directionto its normal rotational direction and when said oblique face of theprominent tooth comes into contact with a tooth of the date crown, thistooth slides over said oblique face which causes a slight tension in theelastic arm and a slight decrease in the width of said cut of the crownof said first drive wheel but without altering the date indication. 24.The calendar mechanism according to claim 13, wherein, when themechanism is operating normally, the driving of the date indicator isphase shifted in time with respect to that of the day of the weekindicator, so that the torques necessary for driving said indicators donot reach their maximum values practically at the same time and preventany malfunction of the timepiece of which they form part.